Lady of the lake

You had been adventuring on your own for a little while and found a cute little lagoon and decided to set up a house close by. It has been a little while sense your house has been finished but you've noticed something weird about the lagoon. There seems to be a mystical feeling around it and you aren't sure why. There have been some unusually coloured scales and a weird lack of fish.
One day you left a couple of things by the pond and when you went to get them the next morning it was gone and replaced with a beautiful shell. This, of course, sparked an idea in your mind so you decided to explore this further....
Niki x reader
This is purely wholesome and nothing more.